The present invention relates to a propeller system, and more particularly to a propeller system for a pusher type counter-rotating propulsion system.
Turboprop engines are commonly designed to drive either a single row of propellers or two rows of counter rotating propellers. The propeller(s) may be mounted forward of the engine (“tractor” installation) or rearwardly of the engine (“pusher” installation). In the pusher arrangement, the engine has an efficient free stream inlet, and the high speed propeller jet does not impinge on airplane or nacelle surfaces, thus avoiding scrubbing drag. Also, a pusher engine installation on the aircraft empennage minimizes cabin noise generated by wing-mounted tractor nacelle engines.
A pusher arrangement, however, may complicate the location for the gas turbine exhaust. One pusher arrangement locates the gas turbine exhaust upstream of the propellers in an annular or lobed configuration. This configuration may require the nacelle skin downstream of the exhaust and a root section of the propeller blades to be designed for elevated temperatures caused by the hot exhaust gases. Furthermore, hot engine exhaust directed past the pusher propeller may increase noise and reduce airfoil life.